It is well known to those skilled in the art that biurets are formed as a side reaction in the formation of urethane foams. This can be represented by the equation: ##STR2##
This reaction is reported to be reversible by heating at temperatures of 110.degree. to 130.degree. C. See Polyurethanes, Chemistry and Technology, Part I by J. H. Saunders and K. C. Frisch, Interscience Publisher. Normally this reaction is reported to be weakly catalyzed by tin catalysts but not tertiary amines.
Since most flexible foams are made with excess isocyanates, biuret linkages are usually present in these foams. The reaction products, represented by ##STR3## possess acid protons and are significantly slower in reactivity toward isocyanates than hydroxyl groups, but under more vigorous reaction conditions are capable of reacting with additional isocyanates.
Typical reactions of isocyanates with ureas can be represented by the following: ##STR4##
There is a general review of the subject in "The Chemistry Of Organic Isocyanates", J. H. Saunders and R. J. Slocombe, Chem. Reviews, Vol. 43, 1948.
It is also known that if hexamethylene diisocyanate is allowed to react with water in a molar ratio of 3:1 a triisocyanatobiuret is formed: ##STR5##
It would be of interest in the art to develop a process to use this side reaction from the production of urethane to make other useful products. It would further enhance the commercial potential of this process if the reaction took place at mild temperatures and ambient pressure without the necessity of a catalyst.
In the instant invention a process has been discovered whereby useful products result from this reaction. The products include flexible, semi-rigid and rigid foams which gel at room temperature. Further, these novel biuret foams were formed without the addition of a catalyst.